do you have to disclose your serial number when selling your laptop

No, but I would insist upon it before buying your laptop, to ensure that it is not stolen, among other reasons.

Are you a buyer? As a buyer, you must place the burden of proof of ownership on the seller. That means the seller must prove to you what he is selling is his to sell, to ensure you are not buying stolen goods, a crime in most places.

Proof of ownership is a dated sales invoice showing the Mac's serial number (all Apple invoices include that information), an AppleCare certificate, original packing materials (all Mac boxes bear its serial number), or a combination of these. There is no consistent central database tying owners to their Mac's serial numbers. Apple does not retain such records, so it's up to the seller to prove it is his to sell, period.

If the seller is unable to prove to your satisfaction that what he is selling is his to sell, run away. There are plenty of legitimate sellers who will be eager to supply this information.

What if you buy a laptop on ebay and aren't provided the original packing materials? I bought and resold a macbook air on Ebay recently. It was working perfectly fine (I have pictures to prove it) right before I shipped it to the buyer. The buyer states it won't turn on and wanted to return it, which I agreed to. When it got here, it does not even boot up at all. I've tried everything. I foolishly did not write down the serial number before shipping. Stupid!!! So now I'm beginning to think he pulled a switcheroo on me. Of course, if I can't locate the serial number, I have no way of proving it.

eBay is a buyer's paradise efemino. You have little choice but to yield to a buyer's will, however unreasonable it may be.

Buyer fraud is rampant. This unfortunate state of affairs has turned away many legitimate sellers of used equipment in recent years. eBay is now dominated by vendors beyond the reach of US law selling $1.99 items with free shipping from Hong Kong.

I am hardly a big seller, but when I sell electronic equipment I include a photograph of the serial numbers or other identifying marks right in the listing. I also put tamper-proof seals on anything that can be opened, and a note in the listing explaining that tampered items will not be accepted for return. I have never had a single return or complaint, but I have no intention of competing with the myriad of bottom feeders offering lower prices. Consider adopting similar practices when selling used Macs. You can include a sceenshot of About This Mac showing its serial number, as well one of the case exterior, to thwart fraudulent attempts to swap logic boards.

Without incontrovertible evidence of buyer fraud, a complaint to eBay will go nowhere. Take back the MBA, switched or not, and absorb the loss. Refusing to cooperate will just get your PayPal account frozen so that you can no longer conduct business.

Isn't eBay wonderful?